1. Field of the Invention
The present invention relates to a multimedia communication controlling system, in particular to, a moving picture reproducing system for reproducing compressed moving picture data that has been inter-frame prediction encoded in a special reproduction mode and a method thereof.
2. Description of the Related Art
As a conventional reproducing system of such moving picture data, Japanese Patent Laid-Open Publication No. 7-143477 has disclosed a motion picture data decoding system that attains smooth video display sufficiently compatible with a frame rate of a video signal by improving an average read rate of coded motion picture data from a picture file device, and that reads encoded moving picture data from the picture file device at high average read rate so as to smoothly display pictures that are satisfactorily corresponding to frames of a picture signal.
In other words, so as to prevent the frame rate from decreasing due to the necessity of setup time such as seek time in reading data from a CD-ROM or the like, a system includes a decoding means for separating moving picture data into a header portion, a timing data portion, and a picture data portion, a header detecting portion for separating the timing data portion and the picture data portion, a register for storing the timing data portion, a timer for supplying time data, and a comparing means for detecting whether or not a stored value of the register accords with the time data and controlling a read control signal corresponding to the detected result. With a start signal, the system starts reading the moving picture data from the decoding buffer. When the system detects the timing data portion, it resumes reading the moving picture data from the decoding buffer and decodes the picture data.
Thus, the system can successively read the moving picture data from the picture data file unit without stopping it. According to the related art reference, since the average read rate of the moving picture signal can be improved to the maximum read rate of the picture data file unit, picture data can be smoothly displayed corresponding to the frame rate of the picture signal.
As a second related art reference, Japanese Patent Laid-Open Publication No. 7-222109 has disclosed a reproducing apparatus for outputting a moving picture from a record medium such as a CD-ROM on which a digital moving picture has been recorded corresponding to, for example MPEG1 system. So as to decrease or increase the update speed of frames of the output picture or output the frames in the reverse direction, the reproducing apparatus comprises a reading means for reading an information sequence from a record medium with a relative motion thereof and outputting a read signal from the information sequence, a signal processing means for separating an I picture from the read signal, a position designating means for designating the position of the information sequence to be read, and a picture outputting means for outputting the separated I picture as a picture signal. The reproducing apparatus can be operated for objects of a user.
Moreover, as a third related art reference, Japanese Patent Laid-Open Publication No. 7-30893 has disclosed an apparatus such as a supervisory camera for supervising a particular position. The apparatus detects an occurrence of an event (such as an intruder) and sends a moving picture thereof for a predetermined time period after the occurrence of the event in a compressed form through a public telephone line. The apparatus successively compresses and encodes an input picture sequence of the moving picture and sends the resultant signal to a transmission line. The apparatus comprises a means for generating an intra-frame encoded picture intra-frame-encoded the moving picture, a means for generating an inter-frame encoded picture inter-frame-encoded the moving picture, a transmission buffer, and an encoding controller. When the apparatus detects an intruder, it traces the photographed moving picture back a little and sends the moving picture to the receive side so that the picture of the intruder can be accurately reproduced.
However, the related art references have the following problems.
In other words, in the conventional multimedia communication systems, when the reproduction mode is changed from a special reproduction mode such as a pause mode or a slow reproduction mode of which compressed moving picture data is reproduced to a normal reproduction mode (play mode), the reproduced picture is skipped for several frames. Next, the reason will be described.
The inter-frame prediction encoded moving picture data is composed of block data of moving picture data as minimum data elements. Each block data starts with a header that contains time stamp information and sequence information.
Conventionally, to simplify the structure of hardware, only header information of the block data is analyzed. At this point, when the reproduction mode of the apparatus is changed from the special reproduction mode (the pause mode or slow reproduction mode) to the normal reproduction mode, block data should be reproduced from the beginning so as to synchronize audio data with video data. This is because since the continuity of data is lost, the reproduction time information should be read to the decoding portion. If the normal reproduction mode is performed while the special reproduction operation is being performed, the moving picture may be skipped for one block in the worst case. In other words, when the moving picture is reproduced in the normal reproduction operation, to synchronize audio data with video data, the buffer memory disposed at the preceding stage of the decoder is initialized. Thus, the moving picture that has not been reproduced is erased. Consequently, the picture data is skipped for several frames.